With respect to an oscillator using a MEMS (Micro Electro Mechanical Systems) resonator, a technique is known in which an oscillation output coil surrounding a wiring in an oscillation circuit in a noncontact manner is provided and an oscillation output is taken out from the oscillation output coil via a buffer amplifier.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2012-70193
[Patent Document 2] Japanese Laid-open Patent Publication No. 2004-198126
However, according to the conventional technique as described above, it is difficult to detect a state of the crystal oscillator before a transition to an output stop state (for example, clock stop) based on the output of the buffer amplifier. It is noted that the output stop of the crystal oscillator may occur suddenly due to abnormality of the crystal oscillator or the like.